Aerodynamics for sprints, hillclimbs and drag racing

[dan]

hardtop,
wing above roofline
flat bottom
vent fender wells, hood, rear bumper
diffuser
front splitter
small mirrors
roll fenders out

[Kiril Varbanov]

The three disciplines you have listed are very different from each other. If it's drag racing, modifications will be different than hill climbing.

As you have already been advised, take off the unnecessary weight - the most killing aspect of a car. Recently I've been driving a stripped-off Audi 90 with about 300 BHP on the crankshaft and this car was scary to drive on the streets.

Hardtop is one of the needed aero tweaks for that BMW, rear wing and diffuser, again, depending on the discipline, front splitter (airdam) as well.

I can estimate some of the improvements in percentage, if done right, but there are too many details missing from the equation, and one of it is the engine's condition. Also, don't forget to invest in proper tires.

[machin]

The whole aero vs mass vs power question in sprints and Hillclimbs was the main reason why I wrote my Virtual Stopwatch App, and I must say the results concur with the comments above; for Hillclimbs and most sprints in the UK you need to be more concerned with the car's mass and weight distribution than the aero side of things... if you can remove something and improve aero then its probably worth doing.... however I'd be wary about adding mass to improve aero, even removing the windscreen on a Westfield doesn't actually improve the performance that much around a tight sprint course like Curborough...

If you want real figures rather than computer generated ones just check out the best times around Curborough in 2011; The 2 litre singleseaters (with wings) were only marginally faster than the 2 litre Westfields (like my avatar; I.e. a very boxy two-seater without wings).

http://www.curborough.co.uk/curbtim.htm

Having said all that, if you are new to sprints/Hillclimbs/racing then you'll see more gains from driver improvement than you will from simple weight or aero improvements...

[Jimster]

I have to say, thank you guys for your responses, I've learned a lot and got some ideas.

Hopefully I can implement them.

I know this might be asking too much, but if you have listed anything, can you please tell me how they would work on the car and how effective they may be, just in general.

[autogyro]

Sell the BMW and buy something that is worth modifying.
With a flexible roadster anything radical will result in far more additional problems to sort than gains made.

[andylaurence]

Given that you state sprints, hillclimbs and drag racing, I'm guessing you're looking at the MSA's Blue Book, where the regs for those disciplines are bunched together. The most obvious point here is that any aero mods on that car will take you from Roadgoing into ModProd (for some mods) or Sports Libre if you want to do most of the things listed so far. If you find yourself sprinting in Sports Libre, you'll find yourself against me and I wouldn't fancy your chances. Most of the competitive cars in class will be a third of the weight, which means you will need triple the downforce to corner at the same pace. That will probably result in triple the drag and that means four times the power to haul it down the straights. You'll need the M Roadster for the 3.2 straight six and forced induction to achieve that much power (800-1000bhp).

Rule number one of competition is to decide what you want to compete in (sprints, hillclimbs or drag racing). Rule number two is to study the class you plan on entering to determine what's currently competitive and why. Rule number three is to buy the most competitive car you can afford.

What are you trying to achieve?

[strad]

Big plus one there Andy.
I remember when I first started drag racing my TR3.
In the AHRA rules you could get away with a lot of mods and still run as stock.
However once I added the 4 carbs they put me into Modified Production where I was at the bottom of the next class up I went from winning every week to getting my ass handed to me each week.

[Kiril Varbanov]

Quite a lot of suggestions with no clear input or requirements from the author.

Just an example of a road car with aero stuff in mind:



Notice the end plates, bargeboards, the high wing, the small winglets, the NACA ducts (submerged inlets) and there's a diffuser on the next picture which I don't have time for. It's Scion, AKA Toyota GT86 prepared for SEMA. I've never been large supporter of tuning shows, but this car, for example, had someone working on its aero ... Purely for illustration purposes.

[Jimster]

That picture is class and explains a lot.

Thanks very much, I've given little input as I don't have that much knowledge in the current matters as I am a beginner.

Can any of you guys give me a bit more knowledge on front diffusers and how they work? I can't find much information on it at all, only a few things come up, but it's simple stuff that I already know such as:
"increases the front downforce substantially, enabling greater braking forces and high speed stability."

Nothing more than that.

[as.racing]

Hi,

You might want to check out my blog: http://www.asracingblog.com as I'm doing a lot of this right now.

For example, Z3 open top vs hard top:





Open top adds about 20% more drag!

Andy